Dielectric films (particularly oxides and nitrides) are widely used in a broad range of applications such as semiconductor chips, magnetic and optical recording, flat panel displays, ink jet printer heads, solar cells, integrated optics, optical films, and hard protective films. Reactive magnetron sputtering which involves sputtering a metal target in argon-oxygen or argon-nitrogen gas mixtures is a commonly used deposition method to produce these films. However, control of such a reactive sputtering process to both maximize the rate of deposition or film formation and to achieve a proper film stoichiometry has been difficult to accomplish.
Reactive sputtering is a very versatile coating technique that allows the preparation of a wide variety of compound materials. However, it has traditionally had one major drawback. When the partial pressure of the reactive gas (e.g., oxygen or nitrogen) reaches the right level to form a stoichiometric film of the metal compound (e.g., oxide or nitride) on the surface of a substrate, it also forms the same metal compound on the surface of the metal target. This, in turn, results in a substantially reduced deposition rate of the films due to low sputtering yield of the metal atoms from the compound part of the metal target. In addition, considerable arcing, leading to a low quality of the deposited films, can be observed on the target under these conditions at high target power densities applied (e.g., during high power impulse magnetron sputtering). Arcing indicates the generation of short circuits between the target (cathode) and an anode or electric ground of vacuum system, caused by the build-up of insulating films on the target. There are two “modes” of operation for reactive sputtering of a metal target to deposit a compound film. For a low flow rate of the reactive gas into the vacuum chamber, the target remains metallic. For a high flow rate of the reactive gas, the target is covered by the compound. Much higher (usually 5 to 10 times) deposition rates are achieved in the “metallic mode” than in the “covered (poisoned) mode”.
A recent development of the well-established magnetron sputtering technique is the high power impulse magnetron sputtering (HiPIMS) which is characterized by target power densities applied during short voltage pulses. The high target power density leads to the generation of very dense discharge plasmas with high degrees of ionization of sputtered atoms. Consequently, film deposition can be carried out at highly ionized fluxes of the target material atoms. This is of significant interest for directional deposition into high aspect ratio trench and via structures, for substrate-coating interface engineering and ion-assisted growth of films. In spite of several successful applications of these systems to reactive sputter depositions of dielectric films, there are still substantial problems with arcing during the deposition processes at high target power densities and with low deposition rates achieved.
Accordingly, there is a need in the art of HiPIMS for a method and apparatus providing effective and reliable control of the reactive sputtering process to achieve high-rate deposition of dielectric stoichiometric films with minimized arcing.